who was the first player to score a hatrick in the world cup and what year was it?

Bert Patenaude.
He scored the first world cup hatrick on July 17, 1930, as the United States played Paraguay in the inaugural World Cup. Bert scored in the 10th, 15th 50th minute to give the US a 3-0 win over the South Americans and claim his spot in world soccer history.

Geoff Hurst's hat trick in 1966 was in the world cup final however the first hat trick in the world cup was in the very first world cup and it was a YANK!!

Patenaude of USA vs Paraguay 1930

Patenaude of the USA vs Paraguay in the first world cup in 1930. Stabile of Argentina got one 2 or 3 days later (vs Mexico, I think). Obviously Geoff Hurst in 1966 is the only player to have scored a hat trick in the final, but then that wasn't your question!!!!

Hirst,who scored a hatick against West Germany in 1966
world cup final.